Evaluation of a sequential extraction procedure for the fractionation of thallium in soils and determination of the content by flame atomic absorption spectrometry

Abstract

To evaluate the existing forms of thallium in soils, a slightly modified and reliable procedure of sequential extraction was developed based on the method described by Tessier et al. (Anal. Chem., 51, 844–851, 1979) using samples of Andosols to which a certain amount of thallium was added and cultivated with rice seedlings during 4 months under water-logging conditions in a pot experiment. Five different thallium fractions extracted in soils by this procedure were identified and the amount of thallium was determined using the method of Asami et al. (Fresenius J. Anal. Chem., 356, 348–351, 1996). A preliminary study showed that the detection limit of the amount of thallium determined by flame atomic absorption spectrometry (FAAS) was 0.2 mg L⁻¹, The MgCl₂ , CH₃COONa, and CH₃COONH₄ extractants exerted significant effects on the extraction of the thallium fractions that were exchangeable and bound to Fe-Mn oxides, but did not affect the extraction of the other thallium fractions, namely the weak acid-soluble fraction, the fraction bound to organic matter and the residual fraction. It was suggested that the chemical behavior of thallium in soils was characterized by ionic and coordination properties, and that soluble thallium added to soil was mainly bound to Fe-Mn oxides. Moreover, the sequential extraction procedure in the present study showed a good recovery ranging from 85 to 101% in relation to the total amount of thallium determined.

Key Words:

• flame atomic adsorption spectrometry
• sequential extraction
• soil
• thallium